RZ Piscium: Strange Star Smashes and Eats Its Own Planets

RZ Piscium and its giant cloud of dust. NASA's Goddard Space Flight Center/CI Lab

Planets are born from dust—but when things in the solar system get really messy, they can end up being turned back into dust as well. And around a weird star scientists call RZ Piscium, located in the constellation Pisces, that phenomenon explains why the star appears to wink, according to a new paper published in The Astronomical Journal.

RZ Piscium posed a mystery to astronomers for a couple of reasons. First there were the winks themselves, which are actually dim periods that can last about two days and result in the star looking 10 times fainter than usual. In addition to this strange behavior, the scientists also knew RZ Piscium was surrounded by a large quantity of warm dust. They knew the dust was there because the star was producing much more infrared light than a typical star, but they didn't know why.

Clouds of dust around stars are perfectly common. After all, that's how Earth and all our neighbors began, back in our own sun's childhood. But stars usually grow out of that phase within a few million years.

To better understand the strange behavior of RZ Piscium, the team behind the new paper decided to try to pin down its real age. Knowing whether it was a young or old star would help explain how unusual the dimming was and why it was happening.

They checked two different stellar aging signs: The amount of x-rays the star is spitting out and the amount of the element lithium still present in the star's body. Both of those decrease as a star ages. For RZ Piscium, the quantities the scientists detected suggested a star between 30 and 50 million years ago, the celestial equivalent of a toddler. (By comparison, our sun is 4.5 billion years old.)

But the young age couldn't explain the quantity of dust—or, planet ingredients—around the star. Even though RZ Piscium is relatively young, it should long ago have aged out of its planet-forming phase. The logical explanation was that the dust was the result not of planets being formed but of planets being devoured.

"The fact that RZ Piscium hosts so much gas and dust after tens of millions of years means it's probably destroying, rather than building, planets," co-author Ben Zuckerman, an astronomer at the University of California, Los Angeles, said in a press release.

Read more: Saturn's Rings Are Made Of a Shredded Moon, Cassini Findings Suggest

That destruction is how RZ Piscium gets its confusing cloud of dust. The star is smashing one or more planets back into their building blocks, just like a toddler in the middle of a tantrum. And the new paper confirmed that it is indeed a cloud of dust that's giving the star its strange blinking pattern.

"Our observations show there are massive blobs of dust and gas that occasionally block the star's light and are probably spiraling into it," lead author Kristina Punzi, a doctoral student at the Rochester Institute of Technology, said in the press release. Additional measurements suggested that cloud is likely about the same distance from the star as Mercury is from our sun, although the researchers couldn't pinpoint precisely how far the planet or planets are in their slow, gruesome demise.